1. Field of the Invention
This invention relates to a method and apparatus for monitoring the compressing force of pelleting press rams.
2. Description of the Prior Art
For the production of tablets, compressing machines are used which have rams which compress the powdery material, from which the tablets are to be produced, in a matrix. Operational breakdowns of various types can occur resulting from the break of a ram or inaccuracies of the compression tools which have developed through wear or as a result of manufacturing tolerances. Furthermore, in practical operation there sometimes occur some inaccuracies in dosing which develop as a result of a faulty setting of the dosing installation and also occasionally there is a double compression of tablets. In order to recognize such operating trouble in good time, it is known to provide tablet compressing machines with a monitoring device for the compression force. Such a known monitoring device for the compression force has wire strain gauges, which are disposed on the carrier of the pressure rolls for the rams. As a result of variable compression forces, variable expansions of the pressure roll carriers are created. As a result of the wire strain gauges such expansions are converted into proportional tension signals. In the known instruments a mean value is formed from the successive pressure force signals, the value of which is monitored in relation to two adjustable tolerance limits. Whenever the mean value exceeds one of the tolerance limits, the machine is disabled. However, it has turned out in practice that not all of the previously mentioned causes for operating trouble can be recognized in time with such measuring processes and instruments, since, for example, in the case of the breaking of a ram of a machine, the mean value does not essentially change since there is a multiplicity of rams. Further, whenever a machine is put in operation which is defective from the very beginning, as when it has a broken ram, such condition cannot be determined subsequently with the known arrangements since this defect does not reveal itself in the manner of a shifting of the mean value.
Therefore, with the prior art arrangement, individual tablets which do not correspond to a certain theoretical weight cannot be sorted out within narrow limits. In the case of a piling up of defective tablets, the known press can be disconnected automatically. However, such an arrangement is not effective in actual practice because outside of the normal dosing and thus weight fluctuations of the tablets, still other values or parameters, such as, for example, tolerances in the length of the ram, a press roller stroke, etc., will influence the compression force. In the case of such defects, with the known arrangement tablets will still be sorted out in an undesirable manner based only on their correspondence to the theoretical weight. Therefore, a supervision and sorting out of the weights of the tablet within narrow limits is not possible with the known arrangement.